Each of these statements highlights a fundamental fact about Earth’s atmosphere. First, the atmosphere experiences “diurnal tides” caused by solar heating, leading to two peaks and two lulls in pressure every twenty-four hours. Second, because gravity pulls the atmosphere downward, the air is most densely packed at sea level, creating maximum pressure. Third, the millibar (mb) is the primary unit of measurement in meteorology, alongside hectopascals (hPa). Together, these facts provide a comprehensive look at how air pressure behaves, how it is measured and why it remains the most important variable in predicting global weather.